A single nucleic acid change from adenosine to guanine (A to G) in "junk" DNA (DNA that scientists used to think wasn't used for anything) reduces the activity of the KITLG gene. This single mutation has been found to change a brunette to a blonde. What's interesting is the mutation doesn't change skin color, eye color, or intelligence (many people often assume that blondes are light-skinned, blue-eyed, and "dumb," but of course this is not always the case!). The mutation doesn't cause every shade of blonde hair - it is responsible for the blonde colors common among many Icelandic and Scandinavian people (and is found in about one-third of northern Europeans). Several other regions of the chromosome also influence hair color.
Scientists didn't find this blonde mutation when studying humans or mice to start - they were studying stickleback fish! These fish can change their color when the water gets more murky or clear. They then studied mice with and without this mutation, and found when the mice have an "A," they are brown, and when they had a "G," they became a lighter brown.
http://www.today.com/health/scientists-discover-blonde-gene-2D79736774
http://news.discovery.com/human/genetics/blonde-hair-gene-identified-140602.htm
Scientists didn't find this blonde mutation when studying humans or mice to start - they were studying stickleback fish! These fish can change their color when the water gets more murky or clear. They then studied mice with and without this mutation, and found when the mice have an "A," they are brown, and when they had a "G," they became a lighter brown.
http://www.today.com/health/scientists-discover-blonde-gene-2D79736774
http://news.discovery.com/human/genetics/blonde-hair-gene-identified-140602.htm